You need high pH for Sulawesi, that's why you shouldn't have substrate to decrease pH. I have been using my RO water with Sulawesi Mineral 7.5 and neutral substrate. Temp is around 28C.
One of the things I want to share is also TDS. Most people say for Cardinal Shrimps you need 120-140 ppm water but if you get your cardinals from a friend who have been keeping them like 250 ppm that's fine also. I have been keeping my Cardinal shrimps in my tank which is around 250 ppm and no issue at all around 1 month.